In order to deploy and insert an electrical stimulator device into a pain patient's spinal canal at a target pain reducing location, a Tuohy needle or cannula is commonly inserted between a pair of the patient's vertebrae. Such needle insertion is commonly precisely guided to assure that the needle's tissue lancing end angularly enters the patient's spinal epidural space without piercing the dura mater sheath which dorsally covers the spinal cord.
Upon such Tuohy needle insertion, an electrode head and wire lead assembly may be threaded therethrough to enter and travel along dorsal aspect of the patient's spinal epidural space. Commonly, such electrode head and lead assembly includes a relatively stiff steel stay which is temporarily received within a stay bore or socket, such stay extending through the electrode wire lead for driving engagement against the electrode head. A pushing action applied to the lead and stay at an input end of the Tuohy needle may effectively drive the electrode head along the spinal epidural space until the electrode head reaches the targeted electrical stimulation location over the patient's spinal cord.
In order to reduce tissue injury at the Tuohy needle injection site and along the travel path of the electrode head within the spinal canal, the selected Tuohy needle preferably is small gauge. Such needle preferably has an inside diameter between 1.3 mm and 1.7 mm, and such needle size imposes limits upon the span, width, or diameter of the electrode head which must initially pass through the needle's bore.
To accommodate for such size and inside diameter restrictions, conventional spinal cord stimulating electrode head components are known to comprise a longitudinally stacked series of cylindrical electrodes. Such electrode configuration maximizes electrode surface contact area for each electrode in accordance with the function, contact area=(l)(d)(π) (where l=the longitudinal dimension of each cylindrically configured electrode and where d=the inside diameter of the Tuohy needle). However, a problem associated with such contact area maximizing cylindrical electrode configuration arises as a result of the electrodes' 360° arcs. Such cylindrical electrodes inherently provide some amount of ventral electrical contact with the pain patient's spinal dura mater. However, the majority of such electrodes' contact areas communicate electrically with the dorsally overlying tissues in the epidural space. Transmission of electrical pulses to such dorsally overlying tissues causes undesirable side effects such as wastage of electrical energy, localized pain, and cramping. In the cylindrical electrode configuration, useful pulses emanate only from electrodes' relatively small ventral contact surfaces.
The instant inventive electrode assembly for stimulation of a spinal cord solves or ameliorates problems and challenges described above by specially configuring a spinal cord stimulating an electrode head to include separately operable and opposing series of electrodes which are situated upon an invertible electrode head.